Theresa May will attempt to head off a rebellion of her Brexit inner cabinet and prevent key leave-supporting ministers from resigning by delaying a final decision on her “customs partnership” model.

The prime minister is expected to keep both of Downing Street’s options for a future customs arrangement with the European Union on the table at least for now as the 11-strong subcommittee meet for talks on Wednesday.

No 10 sources said the prime minister had no plans to “boot out” one customs union option immediately and that officials would continue working on both.

However, May faces a tense showdown with key Brexiters, after the Guardian learned that they are planning to “pointedly and forcefully” persuade her to drop her preferred plan altogether.

Downing Street has spent the last few days intensely lobbying ministers including David Davis, Liam Fox and Boris Johnson on the benefits of the so-called hybrid model, under which the UK would collect EU import tariffs on behalf of Brussels.

But the Brexiters now believe they have the numbers to force her hand, claiming that new home secretary Sajid Javid and defence secretary Gavin Williamson would back them, giving them a majority of six to five in the crunch talks.

Quick guide

What are the UK government's EU customs proposals?

Customs partnership

Under the so-called hybrid model – Theresa May's preferred plan – the UK would collect EU import tariffs on behalf of Brussels. Eurosceptic MPs from the European Research Group, led by Jacob Rees-Mogg have warned No 10 that such a partnership would be considered a red line. Other MPs regard it as the only way of successfully avoiding a hard border in Northern Ireland. But EU officials regard this model as "magical thinking".

'Max-fac'

Brexiters hope to persuade the prime minister to keep the alternative on the table for now – the so-called maximum facilitation (“max-fac”) proposal, which relies on technology, exemptions for small businesses and goodwill to minimise border checks. They argue that "unobtrusive" checks a few miles from the Northern Irish border would not breach the government’s pledge to avoid a hard border. But again, EU officials have rejected this idea, arguing that waivers for small business add up to a smuggler's charter, while technological fixes alone will not be enough to solve the problem.

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It comes after it emerged that 60 Eurosceptic MPs from the European Research Group, led by Jacob Rees-Mogg, have sent May a 30-page report setting out their opposition to the plan.

The group is understood to have repeatedly warned No 10 in recent weeks that the customs partnership would be considered a red line, and crossing it could precipitate the collapse of the government.

One remain-supporting cabinet minister told the Guardian earlier that they expected the prime minister to make a “big push” for her preferred option at the meeting, but Whitehall officials suggested she would stop just short of ditching the alternative.

Brexiter sources claimed that the prime minister had been told eight times by civil servants that her preferred option, which is backed by her top Brexit civil servant Olly Robbins, was unworkable but has continued to stick with it.

The customs partnership has become the most contentious issue in the debate about what kind of Brexit should be pursued, with many MPs regarding it as the only way of successfully avoiding a hard border in Northern Ireland.

Brexiters hope to persuade the prime minister to keep the alternative on the table for now – the maximum facilitation (“max-fac”) proposal, which relies on technology to minimise border checks.

Conservative sources suggested Davis could be prepared to resign if the subcommittee throws its weight behind the prime minister’s option. Insiders said he felt “cut out of the loop” and concerned that he had been effectively replaced by Robbins, who is based in Downing Street.

Liam Fox, the trade secretary, also put down a marker in a BBC interview, insisting that staying in the customs union in all but name would be unacceptable. He refused to deny that he might be prepared to resign if the government pressed ahead.

“That’s worse than the position in which we found ourselves today in the European Union. I don’t think there is a customs union that could ever be acceptable,” he said.

“If we are in a customs union of any sort we will have less ability to shape Britain’s future than we have today. That is not what the public voted for.”

One cabinet minister suggested that ultimately the government would have to settle for a customs union in all but name. “My more pragmatic colleagues understand that, faced with the need to fix this, we will have to reach an agreement that involves significant alignment with Brussels, although we will not technically be in a customs union.”

Cabinet supporters of May’s preferred approach, including Philip Hammond and Greg Clark, believe it has a better chance of avoiding the risk of a hard border in Northern Ireland by allowing traders to move goods freely.

“The technology is challenging for the hybrid option; but if you solve it, it solves the Irish border question”, said a Whitehall source. “Max-fac is probably more technologically straightforward – but it requires borders.”

However, the Brexiters are expected to push back against the idea that maintaining the integrity of the Good Friday agreement requires no infrastructure whatsoever between Northern Ireland and the Republic.

Instead they will argue that unobtrusive checks set a few miles back from the border wouldn’t breach the government’s pledge to avoid a “hard border”.

The departure of former home secretary Amber Rudd removes one of the strongest voices in support of staying in the customs union around the cabinet table. Brexiter sources have suggested that Javid, who reluctantly backed remain in the referendum, and Williamson, considered by colleagues to be pliable, would take a different position.

The subcommittee could also be asked to consider extending membership of the customs union temporarily, while the successor arrangement is implemented. HMRC permanent secretary Jon Thompson told a select committee last September that the customs partnership could take up to five years to be introduced.

On Brexit Williamson told an audience at the Institute of Economic Affairs on Tuesday night that it was “not the time to be timid or go into retreat”.

He added: “As we look to Brexit, it is important that we see our Brexit choice not as a problem, but as an opportunity to expand our role in the world.”

Mujtaba Rahman, managing director of political consultancy Eurasia Group, said with talks in Brussels at a standstill, negotiators would be watching the evolution of the government’s stance closely.

“All eyes in Europe are on the Brexit subcommittee tomorrow, and what it throws up,” he said. But with the next round of talks in Brussels not due until late May, he suggested the prime minister could still delay narrowing her options too much.

Rahman added that by continuing to press the hybrid option, which she knows is unacceptable to Brussels, May is engaged in “stagecraft”, while awaiting the outcome of a series of contentious parliamentary votes on the customs union.

The Guardian understands that neither the customs union, nor Brexit more generally, was brought up at Tuesday’s meeting of the full cabinet. They will be expected to endorse the final option once one is eventually agreed.

The prime minister’s official spokesman said: “We have been absolutely clear that we are leaving the customs union and won’t be joining a customs union.

“We have put forward two proposals for addressing the customs issue in general and they will be discussed by the government further.”